1,721,076 research outputs found
Ring Currents and Magnetisability In C-60
No full textA distributed-origin coupled Hartree-Fock method is used to compute the current density induced in C-60 by an external magnetic field, and hence to plot the pi ring currents and obtain ab initio values of the total magnetisability and nuclear magnetic shielding. Paramagnetic ring currents are associated with pentagons, and interpreted as consequences of strong, local circulations about the formal double bonds of the C-60 framework. The calculated total magnetisability of -370 cgs ppm is strongly diamagnetic and in agreement with the previous extrapolated ab initio result and with and experimental measurement. The calculated central shielding of +12 ppm is in qualitative agreement with the previous extrapolation and the measured encapsulation shift for He-3 in C-60. It is concluded that C-60 is diamagnetic, but that the interpretation of this diamagnetism as a sign of three-dimensional aromatieity is problematic
Two methods of computing molecular dipole and quadrupole derivatives
No full textPolarized basis sets are used to compute dipole and quadrupole derivatives of the hydrides LiH, CH4, NH3, H2O, and HF. Analytic calculation of derivatives is compared with calculation via the dipole and quadrupole electric shielding tensors. With these basis sets, violation of the Hellmann–Feynman theorem is only about 0.01 a.u. in dipole derivatives and 0.02 a.u. in quadrupole derivatives
Anisotropic dispersion forces in methane mixtures
No full textIsotropic and anisotropic dispersion coefficients C6, C7 and C8 are obtained for CH4-CH4, CH4-He, CH4-Ne and CH4-Ar pairs within the ab initio random-phase approximation (equivalent to coupled Hartree-Fock theory) by calculating frequency-dependent dipole, quadrupole, mixed dipolequadrupole and mixed dipole-octopole polarizabilities. The ab initio results are compared with Kirkwood and bond polarizability models and used to parameterise Padeacute approximants for agr, A and E polarizabilities of methane. The near-Hartree-Fock wave-function for CH4 recovers 93 per cent of the experimental dipole polarizability and corresponding fractions of the empirical dispersion coefficients
Ab initio study of a 32-boron cluster: B_32H_32^{2-}
No full textResponse properties of B_32H_32^{2-} are theoretically estimated
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